That yellow plug / welded hole is a temperature input sensor.. A particular model bigport had them in the airbox in FWD format where as most had them in the inlet manifold.. So find yourself an air intake temp sensor + a plug and hook it up. If you don't have an airbox hang it somewhere near the throttle body / pod / whatever you are going to run.
Build is starting to come together nicely, take your time do it right and don't be afraid to ask questions if you need help...